Iwork, Pages for long documents?

I am thinking of starting a writing a book on my new mini (dual core). I have Iwork on the computer. Does anyone have any experience with longer documents using Pages? I would consider a third party program if Pages is not practical (gets clunky on longer documents). Also being new Pages, is the software set up to oraganize longer documents?

Overall as a switcher just trying to stay away from Microsoft products. Purely subjective, based on past experiences. Trying to stay with mac as much as possible.